Many doors are constructed without windows in the top thereof, so that, when they are opened, the person opening the door is not able to see if there is another person on the opposite side of the door. This is particularly a problem with doors which open into or out of stairwells, restroom doors, and the like. In many instances, such as with restroom doors, it is undesirable to make part of the door transparent in order to view someone on the other side prior to opening the door. With respect to doors leading to stairwells, transparent sections in the doors render the doors more expensive than if they were made solid. Additionally, fire codes in some jurisdictions require that doors leading to specific exits be sufficient to prevent the spread of fire from a stairwell, so that doors leading to a stairwell must be of a certain strength.
Some public laws require that certain doors remain open at all times, so that it would be useful to have some means of monitoring the opening and closing of such doors.
Where young children are present, it would be particularly useful to have doors which make an audible sound when opened so that the caregiver is aware of a child's movement through the home, particularly when the door opens into a stairwell. These households may also find it prudent to provide alarms on cupboard doors so that the child's activities are monitored, particularly for cupboards in which potentially hazardous materials are stored.
A number of solutions have been sought for this problem of providing a warning when a door is to be opened. However, none of the known solutions has been sufficiently practical to warrant the inclusion thereof in most doors, as most of them relate to burglar alarms.
D'Almaforte, in U.S. Pat. No. 1,567,921, discloses a door-fastening device which prevents opening of the door as well as providing an audible signal that an attempt is being made to open the door. This device comprises a rod having one end bent so as to engage the keeper plate of a door jamb, a pivoted member secured to the rod, a sliding member positioned in the pivoted member, an audible signal secured to the rod, and a push button controlling the signal. The rod operates the push button, and a spring is provided which is normally adapted to retain the sliding member out of contact with the push button. This device is designed to retain the door in a fastened position rather than merely to warn someone on the other side that the door is to be opened.
Phillips, in U.S. Pat. No. 3,013,523, discloses a door opening alarm for use in combination with a door frame having a lintel and a swingable door hingedly mounted therein. The alarm comprises a bell assembly supported by the lintel above the upper horizontal edge of the door. The bell assembly comprises a horizontal flat U-shaped bracket secured to the lintel. The bracket has horizontally extending arms perpendicularly disposed to the face of the lintel, and a bell supporting member is resiliently supported centrally of the bracket between the arms and a plurality of bells depending from the bell supporting member. Adjustable striker means are mounted on the door in proximity to the bells to sound an alarm only when the door is opened. The striker means are positioned inwardly of the bell supporting member. The adjustable striker means are adjustable in a vertical direction and including a pivoted cam means movable only in one direction. The cam means are provided with inclined surfaces contacting the bell supporting member in both the opening and closing directions.
Sanderson, in U.S. Pat. No. 386,164, discloses an alarm bell for doors comprising a door having a bell mechanism secured upon one side of a door or frame. A push button is provided for operating the bell, the push-button secured on the opposite side of the door or frame and connected through the door or frame by a connecting rod with the bell mechanism. The button has its frame formed with a projecting bevelled guide to aid in centering the button with the opening in the door or frame, and to prevent binding of the operative parts. This alarm requires a push upon the button in order to produce an alarm.
Cook, in U.S. Pat. No. 1,398,362, discloses a detonating alarm which is used as a burglar alarm in windows, doors, and the like. The alarm of this disclosure includes a holder for a detonator, a mounting for the holder including a flat spring, a base for the mounting including an impact receiver against which the holder may throw a detonator, and a trigger carried from the base to engage and hold the holder against spring action. The holder is carried and anchored by the flat spring against movement other than directly to strike the impact receiver when released by the trigger.
Lawlor, in U.S. Pat. No. 517,869, discloses a portable burglar alarm which can be easily transported and which can be applied to doors and windows so as to lock the same and which provides an audible notification when any attempt is made to force open the door or window to which it may be applied. The device consists of a base provided with a shank adapted to be introduced into the space between the door and its casing and to be turned, whereby a stud or tooth on its shank will engage with said casing. An alarm bell is secured to the base, having an alarm mechanism therein. An arm is mounted on the base in bearings, the arm being adapted to be mounted on the base in bearings and adapted to engage with at one and and trip the bell mechanism. A spring is provided for holding the arm normally out of engagement with the bell mechanism. A finger on the arm in the path of the door is adapted to move the arm and trip the bell mechanism when the door is opened and to engage with the bearing so as to lock the door.
Shore, in U.S. Pat. No. 667,799, discloses a combination door lock and alarm which is portable. The device includes a flat, screw-threaded stem having a detent of a door-engaging plate on the stem, outward of the plate, a nut or clamping head on the outer end of the flattened stem, and a bell having the projecting actuating stem and a slitted keeper. The keeper is adapted to embrace the stem and to secure the bell removably in operative position.
Klomfass, in U.S. Pat. No. 1,419,738, discloses a combination burglar alarm and lock which can be attached to a door jamb or casing in position for arrangement either in operative or inoperative position according to the preferences of the occupant of a room. The device comprises a base plate consisting of a hingedly connected attaching and swinging member of which the former is adapted to be secured to the inner surface of a door casing, a stop rod carried by the swinging member for terminal arrangement in the path of a door when the swinging member is disposed in perpendicular relation with the plane of the door, and means for securing the swinging member in its operative position, and consisting of a hook mounted upon the door casing for detachable engagement with the swinging member and arranged in bracing relation therewith.
Lohrens, in U.S. Pat. No. 1,296,982, discloses a combination burglar alarm and lock which cooperates with a door guard of the slotted hasp and latch type. The lock permits the door to be opened a few inches, but prevents the door from being further opened. The alarm comprises a door and its casing of a door guard comprising a hasp, a latch on the door for association with the hasp to lock the door in either closed or partially open position, means for mounting the hasp carried by the casing to permit limited bodily movement as well as pivotal movement thereof, a signal, and means actuated by the bodily movement of the hasp to initiate the signal.